1. Field of the Invention
The present invention relates to a method and an apparatus for adjusting the relative height between two sets of magnetic head groups mounted on actuators. More particularly, the present invention relates to a method and an apparatus for adjusting the relative height between two sets of magnetic head groups at the time of recording in a rotary head type magnetic recording/reproduction apparatus such as a helical scan type video tape recorder (VTR).
2. Description of the Background Art
In recent years, there has been efforts to significantly increase the density of recorded information in a magnetic recording/reproduction apparatus, resulting in reduction of the track width. For example, the track width is 5 .mu.m in a LP mode of a home use digital VTR. Such reduction of the track width causes strict conditions on a magnetic head to carry out a satisfactory tracking operation. More specifically, when a signal is to be reproduced from a track having the width reduced in a conventional type of magnetic recording/reproduction apparatus having the magnetic head fixed to the rotary drum so that the magnetic head cannot move in the direction of the track width, deviation occurs in the tracking of the magnetic head, so that a sufficient reproduced output cannot be obtained from the magnetic head.
This deviation in tracking is considered to be caused by the so-called track bent that occurs during recording. Because this track bent is inherent in each magnetic recording/reproduction apparatus, deviation in tracking caused therefrom becomes too great to be neglected particularly when the relevant track is reproduced by a magnetic recording/reproduction apparatus different from that used for recording.
In view of the foregoing, a magnetic recording/reproduction apparatus is disclosed in, for example, U.S. Pat. No. 4,237,399. According to this magnetic recording/reproduction apparatus including a dynamic tracking system, a magnetic head displaceable in the track width direction by an actuator such as of piezoelectric elements is used. The relative position error of a magnetic head with respect to a track on a magnetic tape is detected on the basis of a signal reproduced from the magnetic head, whereby the position of the magnetic head in the track width direction is controlled by a closed loop according to the detected relative position error.
There are various methods of detecting a relative position error signal of a head with respect to a track on a magnetic tape during reproduction. One typical method is the so-called pilot signal system. According to this pilot signal system, a pilot signal having a different frequency for each track is recorded to be superimposed on a main signal. At the time of reproduction, pilot signal crosstalk components are respectively extracted from tracks located at both sides of a certain track to compare these crosstalk components, whereby the amount of position error of the magnetic head and a polarity representing the direction of deviation of the magnetic head from the track can both be detected.
If a magnetic head is commonly used for recording and reproduction, the cost can be reduced by virtue of the smaller number of heads used and by simplifying the drum structure. However, when a magnetic head is provided on an actuator as described above, the height of the head cannot be determined at the time of recording. For example, when there is deviation in the relative height between the two sets of magnetic heads mounted on separate actuators, a track of a predetermined track width and a predetermined track pitch cannot be formed. As a result, sufficient reproduced output cannot be obtained from a track that has the track width reduced. This becomes more noticeable as the track width (track pitch) becomes smaller.
A method of adjusting the relative height of two sets of magnetic heads mounted on separate actuators is disclosed in, for example, Japanese Patent Laying-Open No. 2-44514.
FIG. 37 is a bottom view of a rotary drum showing the head arrangement of such a conventional magnetic recording/reproduction apparatus employing this head height adjusting method. Referring to FIG. 37, magnetic heads 200A and 200B are installed on actuators 201A and 201B, respectively, that are displaceable in the track width direction. FIG. 38 is a schematic diagram for describing the principle of a conventional method of adjusting the head height. A conventional method of adjusting the height of a head will be described hereinafter with reference to FIGS. 37 and 38.
First, a magnetic tape 202 is set to a running stop state. In this state, a record track 200a is formed on magnetic tape 202 at the first half of a scanning operation by magnetic head 200A. Then, a same record track 200a is reproduced at the first half of a scanning operation of the same track on magnetic tape 202 by magnetic head 200B. Here, actuator 201B on which magnetic head 200B is installed is displaced so that magnetic head 200B follows record track 200a. From this amount of displacement, the amount of track deviation , i.e. the amount of deviation of height of magnetic head 200B with respect to magnetic head 200A is obtained. Then, at the latter half of this scanning operation on magnetic tape 202 by magnetic head 200B, a record track 200b is formed. Then, magnetic head 200A scans the same track on magnetic tape 202. At the latter half of this scanning operation, record track 200b is reproduced by magnetic head 200A, and the amount of track deviation, i.e. the amount of deviation of height of magnetic head 200A with respect to magnetic head 200B is obtained in a similar manner.
By obtaining the average of these two height deviation amounts and displacing one magnetic head according to the obtained value, the relative height difference between magnetic heads 200A and 200B becomes zero. Therefore, a track can be formed that has a proper track width and a proper track pitch in recording a signal.
The above-described conventional method of adjusting the head height has the problems set forth in the following. Since detection of the amount of relative height deviation between heads is carried out on the basis of only one track, the detected error is not averaged and sufficient accuracy cannot be obtained.
Furthermore, because the magnetic tape is held in the run stop state, the contact between a magnetic tape and a magnetic head is often unstable. It cannot be identified whether a change in a reproduced output is caused by deviation in the relative height between the heads, or by unstable tape/head contact.
Furthermore, because a magnetic tape is held in the run stop state, the position in the width direction and the longitudinal direction of the magnetic tape is apt to become unstable. This causes a change in the position of a track to be used as a reference, resulting in degradation of the detected accuracy of the amount of relative height deviation between heads.